Abstract: Objective To investigate the relationship of CAG repeat length polymorphism in the androgen receptor （AR） gene to the development of acne. Methods A total of 238 patients with acne vulgaris and 207 healthy human controls in Northeast China were included in this study. Genomic DNA was isolated and purified from the blood of these subjects. The CAG repeat lengths in the AR gene were analyzed by somatic microsatellites （STRs）. Results A significant difference was found in the CAG repeat number between the male acne patients （22.70 ± 3.09） and male controls （23.48 ± 2.83, P = 0.046）, but not between the female cases and controls （23.41 ± 2.87 versus 23.85 ± 0.21, P = 0.12）. In order to assess the risk associated with CAG repeats, the male and female subjects were dichotomized based on the median repeat length in the corresponding control group as the arbitrary cut-off point. Those men and women with a short CAG repeat length （< 23 in men, and < 24 in women） had a significantly increased risk for acne than those with a long CAG repeat length （men: 95% confidence interval, 1.21-3.54, OR = 2.07, P = 0.008; women: 95% confidence interval, 1.18-3.56, OR = 2.05, P = 0.01）. Conclusions This study strongly indicates that the CAG repeat length in AR gene is associated with the development of acne in Northeast China, and those men with a short CAG repeat length seem to have a high risk for acne. Consequently, CAG repeat length may serve as a genetic susceptibility marker.